The objective of this research program is to elucidate biochemically and morphologically the fundamental lesion(s) of pulmonary oxygen toxicity in the newborn and to characterize and measure the development and progression of this lesion(s) and its sequelae so that agents potentially capable of ameliorating or preventing the acute and chronic damage to the lung can be rigorously evaluated. It is proposed (1) to determine when the newborn mouse becomes "adult" in its mortality response to continuous exposure to 100% oxygen and to characterize the milieu that exists at that time, (2) to evaluate the electron microscopic and histochemical characteristics of the alveolar and capillary basal lamina in the normal developing mouse lung, the 100% oxygen exposed developing lung, and the "adult" mouse lung and the relationship of age dependent differences on survival in 100% oxygen, (3) to quantitate the reactive changes in specific cell types of the newborn lung resulting from exposure to 100% oxygen, (4) to quantitate the changes in interstitial tissue, alveoli, capillaries, and scar tissue in the newborn mouse lung exposed to 100% oxygen, (5) to measure the effect of superoxide dismutase and other drugs potentially capable of protecting against the cellular and tissue effects of pulmonary oxygen toxicity at normal atmospheric pressure, (6) to continue to define the natural history of the disease in the newborn lung by (a) measuring biochemically and morphometrically and evaluating morphologically the parameters indicative of the completeness of recovery from both short term (4-7 days) and longer term (3-4 weeks) exposure to 80-100% oxygen and by (b) measuring biochemically and morphometrically and evaluating morphologically the effect of exposure to oxygen concentrations below 100% (40,60,80%) for prolonged periods of time (1, 2, 4, 6, and 8 weeks).